Axes in SketchUp
In SketchUp there are a number of basic concepts that, once understood, make it much easier to work in the 3D space of the drawing window. One of these is the axes. The Global axis lines are the red, green and blue lines that are normally seen in the drawing window. The point where these lines cross is called the Origin. The red line is the X-axis, green is the Y-axis and blue is the Z-axis. The Z-axis is the vertical one. Components are get their own axes. We’ll talk about them later. The solid axis lines are the positive direction while the dotted axis lines are on the negative side.
The orientation of the Standard Views is related to the the global axes. If, for example, you choose the Front View, the X-axis (red line) will run horizontally across screen and the Z-axis (blue line) will run vertically. The Y-axis (geen) will run away from you toward the background. I generally draw models so that their front is aligned with the red axis and on the solid green side of it so that when I choose that front view I’m actually looking at the front of the model.
If you are drawing a model in which the compass directions are important, by default, North is the positive Y direction and East the positive X direction. The global axis orientation can be changed as can the compass orientation but I generally find it easier to just work with them as they are.
Components also have axes. When the component is created, the axes are aligned with the global axes and the origin is placed in the corner of the bounding box nearest the global origin. The component axes impact the way materials get applied to the component’s faces. They also affect the size of the bounding box which is used in plugins such as Cutlist and Layout to determine the amount of wood needed.
For components that are made for use in other models such as door and drawer pulls, it is useful to remember that the component’s alignment is determined by its axes relative to the global axes and the component’s origin is the insertion point. This is the point you hold onto when bringing the component in from the component library. Axis alignment and origin placement can be adjusted if needed.
Tim Killen and I both tend to work in a similar manner when drawing. We draw components in situ as much as possible. One of the results of this is that the component’s axes are automatically aligned with the global axes from the beginning. For most components that works perfectly however there are some cases where it doesn’t. As examples consider the sloped front of a slant front desk, a chair seat that is higher in the front than in the back or a rafter for a shed roof.
With the geometry drawn in place, the bounding box will be much larger than the actual geometry and the axes won’t be aligned to the sides of the component. These components will require the axis to be changed to ensure they are properly reported in a cutlist and/or to make them easier to texture. Of course the part could be drawn so it is aligned to the globabl axes and then, after making the component, it could be rotated into place. It is easier to accurately draw the part in place with its final orientation and then correct the axis alignment after creating the component.
In the following video, I’ve tried to illustrate some of the ways to work with compoent axes.